The rupture of a cruciate ligament in the knee of a human or other animal is a relatively common injury. Traditionally, such injuries have been addressed by rebuilding or replacing the ruptured ligament. However, if there is an underlying biomechanical or genetic problem that caused the ligament to rupture in the first place then the repaired ligament will be at risk of rupturing again in the future.
In order to solve this problem a procedure known as a tibial tuberosity advancement was developed. Rather than simply rebuilding or replacing the damaged ligament, this procedure seeks to neutralise the forces experienced by the cruciate ligament during motion by changing the angle between the patella ligament and the tibial plateau. This changes the way that the quadriceps muscle and patella tendon pull on the tibia such that the quadriceps muscle and patella tendon pull the tibia back into place, thus taking over the function of the torn cruciate ligament. This procedure is performed by cutting a portion of the tibia comprising the tibial tuberosity from the tibia and then reattaching the tibial tuberosity to the main portion of the tibia with a spacer, known as a cage, arranged between the two portions of bone. The spacer acts to advance the position of the tibial tuberosity forward, hence the name of the procedure being a tibial tuberosity advancement. As the patella tendon naturally extends from the tibial tuberosity, by advancing the tibial tuberosity the positioning of the tendon is altered so that the knee joint can function well.
However, the known cages used for spacing apart the two portions of bone are not particularly versatile. The known cages may therefore be relatively difficult to implant. Also, a relatively large inventory of components may be required in order to cover the range of knee joints in which a cage may be required to be implanted.
It is therefore desired to provide an improved cage assembly for use in tibial tuberosity advancements.